AJP - Regulatory, Integrative and Comparative Physiology, Vol 255, Issue 5 846-R850, Copyright © 1988 by American Physiological Society
Fetal and adult urine flow and ANF responses to vascular volume expansion
R. A. Brace, L. K. Miner, A. D. Siderowf and C. Y. Cheung
Department of Reproductive Medicine, University of California, San Diego, La Jolla 92093.
Isotonic saline (2% of body wt) warmed to body temperature was infused
intravascularly over 10 min into chronically catheterized, near-term fetal
sheep and into nonpregnant adult sheep. Although both groups of animals
underwent the same initial increase in urine flow rate relative to body
weight, the diuresis was significantly more prolonged in the adult compared
with the fetus. The adult demonstrated a sustained increase in plasma
atrial natriuretic factor (ANF) concentration with a suppression of plasma
renin activity (PRA) and plasma arginine vasopressin (AVP). In the fetus,
only a transient rise in plasma ANF with no change in PRA or AVP occurred.
The increases in blood volume and arterial pressure were significantly
greater in the adult compared with the fetus, but the venous pressure
changes were the same. Thus it appears that fetal and adult kidneys have
the same initial urine flow response to rapid vascular volume loading
presumably due to a pressure diuresis and elevations in ANF. The more
prolonged diuresis in the adult appears attributable to more extensive and
prolonged changes in plasma hormone concentrations. The latter, in turn,
may be due to the greater intravascular retention of the infused fluid in
the adult than in the fetus.
